A universal mobile telecommunications system (UMTS) is a third generation mobile communication system utilizing a WCDMA air interface technology. Therefore, the UMTS system is usually referred to as a WCDMA communication system. A structure of the UMTS system is similar to that of a second generation mobile communication system, which includes a radio access network (RAN), a core network (CN), and a user equipment (UE). The RAN is adapted to perform all wireless-associated functions. The CN is responsible for performing functions of user location management and service management within the UMTS system, and realizing exchanging and routing functions with an external network. The CN is categorized into a circuit switched domain (CS) and a packet switched domain (PS) in logic.
In order to enhance the performance of the UMTS system, currently, an international program of system architecture evolution (SAE) is in progress. FIG. 1 is a schematic structural drawing of a UMTS system utilizing SAE. As shown in FIG. 1, the system includes a UE 11, an enhanced UMTS terrestrial RAN (EUTRAN) 12, and a CN 13.
The UE 11 and the EUTRAN 12 are connected through an LTE-Uu interface. The EUTRAN 12 includes an evolved node B (briefly referred to as ENB), or may also include other nodes. In the subsequent descriptions, all these nodes are represented by ENBs, which are adapted to receive messages from the UE 11, and to select corresponding network equipment in the CN 13 according to the load balance information. The CN 13 is responsible for performing functions of user location management and service management within the UMTS system, and realizing exchanging and routing functions with an external network. The CN 13 includes a mobility management entity (MME) 131, a serving SAE gateway 132, a packet data network (PDN) SAE gateway (PDN SAE GW) 133, a policy control and charging rules function (PCRF) 134, and a home subscriber system (HSS) 135.
The MME 131 has a control plane function, which is adapted to perform functions such as control plane message processing, mobility management (recording location information of the UE), paging, and authentication with the UE. The MME 131 is connected to the EUTRAN 12 through an S1-MME interface.
The serving SAE gateway 132 has a user plane function, which is adapted to transfer data of the UE. The serving SAE gateway 132 is connected to the EUTRAN 12 and the MME 131 through an S1-U interface and an S11 interface respectively. The MME 131 together with the serving SAE gateway 132 is similar to a serving general packet radio service (GPRS) support node (SGSN) of a UTRAN. As shown by the dotted lines in FIG. 1, the serving SAE gateway 132 is connected to the SGSN through an S4 interface, and the MME 131 is connected to the SGSN through an S3 interface based on a GPRS tunneling protocol (GTP).
The PDN SAE GW 133 has functions of policy enforcement, packet filtering, and the like. The PDN SAE GW 133 is connected to an external data network through an SGi interface, which is similar to a gateway GPRS support node (GGSN) of the UTRAN.
The PCRF 134 is adapted to perform policy associated control functions. The PCRF 134 is connected to the PDN SAE GW 133 and an external data network through an S7 interface and an Rx+ interface respectively.
The HSS 135 is adapted to store users' subscription data. The HSS 135 is connected to the MME 131 through an S6a interface.
In practical applications, the serving SAE gateway 132 and the PDN SAE GW 133 may be located at the same physical node, or may also be located at different physical nodes. Similarly, the MME 131 and the serving SAE gateway 132 may be located at the same physical node, or may also be located at separate physical nodes. When the serving SAE gateway 132 and the PDN SAE GW 133 or the MME 131 and the serving SAE gateway 132 are located at the same physical node, interface signaling between them are converted into internal node messages.
In a conventional UMTS system mode, one access network node can only be connected to one CN node. In a UMTS system utilizing SAE, one access network node is able to be connected to one or more CN nodes, that is, a Flex technology. Flex refers to intra-domain connection of RAN nodes to multiple CN nodes. That is, within one pool, multiple CN nodes (for example, MMEs) are connected to all EUTRAN nodes (for example, ENBs) within the pool. When one UE enters the pool initially, the EUTRAN node is able to select one CN node according to, for example, load balance principle. In such a manner, as long as the UE does not move out of the pool, the access of the UE is always anchored at the selected CN node.
FIG. 2 is a schematic structural drawing of a pool in a UMTS system utilizing SAE. As shown in FIG. 2, a plurality of MMEs forms one MME pool. A plurality of serving SAE gateways forms one serving SAE gateway pool. ENBs within an area of the MME pool are connected to all the MMEs within the MME pool. Similarly, ENBs in an area of the serving SAE gateway pool are connected to all the serving SAE gateways within the serving SAE gateway pool. When the UE initially enters a certain pool area, it may select one MME or serving SAE gateway with a low load in the pool according to, for example, the load balance principle. Once the UE has selected an MME or serving SAE gateway within the pool, as long as the UE moves within the pool, the selected MME or serving SAE gateway does not need to be replaced, thereby avoiding frequent relocation of the CN nodes, until the UE moves out of the pool area. For ease of the illustration below, the MME pool is taken as an example for illustrations as follows. The serving SAE gateway pool is similar to the MME pool. In such a manner, when a failure occurs to the CN node within the system, the UE may select another node within the pool, so as to avoid a single-point failure caused by the UE failing to access the whole failed CN node area.
A pool area includes a complete tracking area (TA). Pool overlapping that one ENB belongs to a plurality of pools (for example, an MME pool and a serving SAE gateway pool) might occur.
FIG. 3 is a schematic structural drawing of an MME pool in the prior art. As shown in FIG. 3, a plurality of MMEs forms one MME pool 1. Another plurality of MMEs forms one MME pool 2. An ENB 1 and an ENB 2 belong to the MME pool 1, and have interfaces with all MMEs in the MME pool 1. An ENB 4 and an ENB 5 belong to the MME pool 2, and have interfaces with all MMEs in the MME pool 2. An ENB 3 belongs to the two MME pools. That is, the ENB 3 has interfaces with all MMEs in the MME pool 1 and the MME pool 2, which is an overlapping part of the MME pool 1 and the MME pool 2. When a UE enters the ENB 1, it selects one MME from the MME pool 1. During the process of moving from the ENB 1 to the ENB 2 and to the ENB 3, the UE does not need to change the MME. When the UE enters the ENB 4, as the ENB 4 only belongs to the MME pool 2, and has no interface with a source MME, the UE needs to select an MME in the MME pool 2 again. When the UE returns from the BNB 4 to the ENB 3 again, as the ENB 3 has an interface with the MME pool 2, the UE does not need to select an MME again. Only when the UE enters the ENB 2, an MME needs to be selected again, so that MME relocation occurs. If the ENB 3 does not have an interface with the MME pool 2, when the UE moves back and forth between the ENB 3 and the ENB 4, ping-pong MME relocation needs to be initiated. That is to say, the pool overlapping avoids ping-pong MME relocation or serving SAE gateway relocation.
TA overlapping and Multi-TA are two possible solutions in the current TA concept. The TA overlapping indicates that only one TA can be assigned to one UE each time. An ENB may belong to two TAs at the same time. When the TA is changed, a TA update (TAU) is initiated. The Multi-TA indicates that one UE may be assigned with a plurality of TAs (a TA list), and each cell only broadcasts one TA identification (TA ID). In such a manner, when the UE moves within the assigned TAs, no TAU needs to be initiated (except the circumstance that a periodic location update needs to be initiated). If the UE moves to one TA that is not in the TA list of the UE, a TAU needs to be initiated. After the TAU, the UE receives a new TA list.
FIG. 4 is a schematic structural drawing of a pool combined with Multi-TA in the prior art. As shown in FIG. 4, when the pool overlapping does not exist in a system, for example, an MME pool 2 is not connected to ENB 2/3 of a TA 2 (not shown), the UE is assigned with a TA list {TA 1, TA 2} in an MME pool 1. When the UE moves to a TA 3, a TAU is initiated, and the UE is assigned with a TA list {TA3, TA4}. In such a manner, when the UE moves back and forth between the TA 2 and the TA 3, ping-pong TAU and ping-pong MME relocation may occur.
When the pool overlapping exists, for example, the MME pool 2 is connected to both the ENB 2/3 of the TA 2 (as shown by dotted lines in FIG. 4), the UE may be assigned with a TA list {TA 1, TA 2} in the MME pool 1. When the UE moves to the TA 3, the UE may be assigned with a TA list {TA 2, TA3, TA4}. The ping-pong TAU and the ping-pong MME relocation are avoided when the UE moves back and forth between the TA 2 and the TA 3.
In the examples above, as a concept of a pool is introduced, when the UE moves into a new area or is attached or handed over, a problem of how the UE selects a suitable network node is involved. In the prior art, the UE simply selects one node with a low load from a pool according to the load balance information, which may cause the following problems. In the prior art, a situation that one ENB belongs to a plurality of pools is not considered at all. If the selection is improper, the CN node relocation probably occurs. In addition, different nodes between the pools or within one pool may have different capabilities. In order to reduce network cost and increase an operation efficiency of the network, a manner of selecting a suitable node for the UE to meet the requirements of the services needed by the UE needs to be considered.